Fair Value (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	$ 7,106,142,000		$ 7,112,474,000
expense related to other repossessed assets	0
Alternative Investment	21,795,000		21,522,000
Loans Held-for-sale, Fair Value Disclosure	17,766,000		31,666,000
Impaired Financing Receivable, Carrying Value	$ 95,445,000		103,021,000
Discount percentage applied to real estate appraised values	15.00%
Discount percentage applied to lot development appraised values	6.00%
Partial Charge-Offs On Impaired Loans	$ 589,000		655,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	4,962,000		5,434,000
Impaired Financing Receivable, Related Allowance			5,434,000
Impaired Loan Fair Value	7,484,000		6,924,000
Partial Charge-Offs On Impaired Loans carried at Fair Value	203,000		269,000
Book Value Of Impaired Loans Carried At Fair Value	7,890,000		8,256,000
Impaired Financing Receivable, carried at fair value, related expense	900,000	$ (57,000)
MSR recorded at lower of cost or fair value	13,635,000	8,768,000	12,210,000	$ 10,070,000
Mortgage Servicing Rights Fair Value	13,300,000		12,200,000
Valuation allowance of MSR	2,337,000	2,351,000	3,189,000	$ 825,000
MSRs recorded at cost	328,000		31,000
Changes due to fair value adjustments	(852,000)	1,526,000
Other Real Estate, Foreclosed Assets, and Repossessed Assets	$ 844,000		$ 1,431,000
Percent of OREO held at fair value	87.00%		51.00%
Other Real Estate, Foreclosed Assets, and Repossessed Assets, Fair Value	$ 735,000
OREO valuation adjustments	0	2,000
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	6,200,000
Alternative Investment, income recognized	1,400,000	$ (204,000)
Fair Value Measured at Net Asset Value Per Share [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Alternative Investment	15,600,000		$ 15,400,000
Commercial Receivables, excluding Commercial, Financial, and Agricultural [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	406,000		1,332,000
Financing Receivable, not collateral dependent [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	4,556,000		4,102,000
Fair Value, Nonrecurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans Receivable, Fair Value Disclosure	$ 7,484,000		$ 6,924,000